Brain and Body

Why Does Coffee Make You Poop?

December 21, 2015 | Kelly Tatera

A cup of coffee
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And other bizarre body phenomena explained.

Our bodies do some pretty weird things sometimes, but for most behaviors, there’s a reasonable  explanation. For instance, when one person yawns, why does it start a chain reaction? Or is there a reason we see those little spots of light when we close our eyes?

We’ve compiled a list of some of the strangest body phenomena along with scientific explanations for them. So rest assured knowing that your body’s odd behaviors are completely normal.

Why does coffee make you poop?

If your morning routine involves coffee, there’s a good chance you’ve experienced the sensation of needing to visit the bathroom after a cup or two. Coffee contains about 2,000 compounds, so scientists aren’t certain which one causes the laxative effect so quickly. However, they know how this coffee compound works within the body — it increases the levels of a different compound called cholecystokinin, which regulates how often we have to go. Levels of gastrin, a compound found in the colon, also increase.

Although it seems like lots of people report this effect, the American Chemical Society reports that only a third of the population experiences this reaction to coffee.

Why do you twitch when you’re falling asleep?

You’re laying in bed watching Friends reruns on Netflix and feel your eyes getting heavy. You’re starting to doze off a little bit, but all of a sudden your whole body twitches and wakes you back up.

Why does this happen? In scientific terms, the random twitching is known as a hypnagogic jerk, or an involuntary muscle spasm that happens while someone is drifting off to sleep. The hypnagogic state describes the transition between wakefulness and sleep, and the muscle spasms can either be spontaneous or induced by external stimuli like sound and light.

Scientists report that these sleep jerks happen to about 60 to 70 percent of people, and that certain factors like stress, caffeine, and fatigue may increase the frequency or severity of them.

Why are yawns contagious?

It’s not just humans that can’t seem to help yawning once someone else does it — scientists have observed this “contagious yawning” in chimps, baboons, bonobos, and wolves too, according to Mental Floss. Studies have shown that even just seeing pictures or videos of other people yawning can provoke the contagious yawns.

Contagious yawning remains somewhat of a mystery to scientists, but recent studies have related the yawning phenomenon to our levels of empathy. It sounds odd, but whether you’re likely to catch contagious yawns could be linked to how you understand and connect with the emotional states of others. This would explain why contagious yawning is associated with the parts of the brain that deal with empathy.

Why do you see spots of light when you close your eyes?

Sometimes when you close your eyes, you probably notice mysterious colorful blobs showing up on the back of your eyelids. No, it’s not an illusion, and the phenomenon is coming from inside your own eyes. Those bizarre spots of colorful light are called “phosphenes,” and they’re a result of our eyes emitting biophotons, or biologically produced light particles.

Depending on where the phosphenes originate, they can come in a variety of colors, shapes, and patterns. Different molecules and atoms emit photons of different wavelengths, and scientists have also found that different areas of the visual cortex in the brain create specific phosphene shapes.

Why does asparagus make your pee smell weird?

This is a weird one, but rumor has it that eating asparagus can result in some odd-smelling urine. According to WebMD, this effect is totally normal and has actually been observed for centuries.

Some studies have reported that up to half of the population experiences pungent pee after eating asparagus, but it’s not those people’s bodies that are generating the unpleasant smell. The vegetable’s sulfurous amino acids break down into odorous chemical components in all people, but it’s because these components are airborne that they can lead to smelly pee. As soon as 15 minutes after eating asparagus, this odor can waft upward as urine leaves the body.

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